Miss Winfrey repeatedly has told her 14 million Twitter followers about Ms. DuVernay’s latest film, “Middle of Nowhere,” which expanded to 14 more cities Friday after opening in six theaters the previous week. She described the film as “powerful and poetic.”

The 40-year-old Ms. DuVernay, whose easy smile, animated energy and passionate dedication make her seem a decade younger, beams as she says, “I’m living my dream.”

There’s a massive congratulatory bouquet of orchids on the desk in her small office overlooking Van Nuys Boulevard. A bookshelf is crowded with recent awards, including the best director prize she won at the Sundance Film Festival earlier this year. (She was the first black woman ever to win.) Posters from her first documentary and first narrative feature adorn the walls. A magnum of Moet with a big gold bow on top sits on the floor.

Just a little over a year ago, Ms. DuVernay was a Hollywood publicist focused on other people’s movies. Through her namesake public-relations firm, she helped develop release strategies for films such as “The Help,” “Invictus” and “Dreamgirls,” while quietly dreaming of telling her own stories.

In 2002, the Los Angeles native and UCLA graduate sat down and wrote “Middle of Nowhere,” a story set in her hometown about a young medical student coping with her husband’s recent eight-year jail sentence.

“Where I’m from, it’s impossible not to look at this real epidemic in black and brown communities of incarceration and the women who are left behind,” said Ms. DuVernay, who grew up in and around Compton.

She pitched the script to some of her Hollywood colleagues, but got no traction and shelved it.

“Everyone in town has a script in the drawer, so I just joined the club,” she said.

Undaunted, she wrote a second screenplay, “I Will Follow,” which became her first feature — produced in 2011 with her own $50,000 savings. It earned raves from Roger Ebert and nearly tripled its budget in ticket sales.

“It proved there was an audience for low-budget, thoughtful films for women and people of color,” she said.

So she went back to her original script with new confidence, making the film last year for around $200,000. Set against a social-justice backdrop of prison inequity, the film is more about the interior lives of the women it features.

“It’s really trying to get to those quiet spaces which are just not being depicted in cinema,” she said. “I purposely didn’t want it to feel like castor oil or medicine, which is something that we get specifically when we’re dealing in African-American cinema. It’s always a lesson, or a history lesson. This is a beautiful love story, and the sister’s got a man who’s locked up. Let’s explore what that is.”

Bringing light to untold stories and broadening the scope of black independent film is what moves Ms. DuVernay to distribute her own projects and those of other black filmmakers.

“Black audiences are not used to art-house fare because they’ve not had any kind of diet of it. It’s not been provided to them,” she said. “And independent audiences are not used to black fare.”

She wants to cultivate and educate both audiences through her own films and AaFFRM.

“There’s something very important about films about black women and girls being made by black women,” she said. “It’s a different perspective. It is a reflection as opposed to an interpretation, and I think we get a lot of interpretations about the lives of women that are not coming from women.”

Ms. DuVernay said she is convinced that stories from underrepresented populations will find audiences in this digital age, just as her films have.

“It’s easier to get your hands on a camera now, easier to make a film, easier to get and find an audience and new ways to reach people through digital,” she said.